Dynamic hq for closed loop control

ABSTRACT

A method of controlling a blood pump having a predefined hydraulic performance including at least from the group consisting of estimating and measuring an instantaneous flow rate during operation of the blood pump at a predetermined rotational speed of an impeller of the blood pump, the instantaneous flow rate including a plurality of flow rate data points. The plurality of flow rate data points define a trajectory around at least one from the group consisting of an operational point of a predefined pressure-flow curve associated with the predetermined rotational speed of the impeller of the blood pump and a target operational point of a target pressure-flow curve different than the predefined pressure-flow curve. The predetermined rotational speed of the impeller is adjusted until the plurality of flow rate data points define a predetermined trajectory around at least one of the operational point and the target operational point.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.16/148,312, filed Oct. 1, 2018, which claims the benefit of U.S.Application Ser. No. 62/571,964, filed Oct. 13, 2017.

FIELD

The present technology relates to a method for automating speed changesin a rotary blood pump to produce a desired pressure-flow relationship.

BACKGROUND

Rotary blood pumps have inherent hydraulic performance that is unique tothe design of each pump. This performance is summarized by a pump'spressure vs. flow (HQ) curves, a series of curves, which vary by pumpspeed. An exemplary HQ for the HVAD® pump (FIG. 1) sold by HeartWare,Inc. is shown in FIG. 2. The behavior of a pump in a steady-state orpulsatile environment will depend on the shape and values of thesecurves. However, clinicians and physicians may be desirous of aparticular HQ curve different than the inherent HQ curve of the pumpdepending on, among other things, the patient's needs and associatedadverse events. For example, as shown in FIG. 2, an exemplary target HQcurve is shown superimposed on the inherent HQ curves of the HVAD pump.Prior approaches to achieve a target HQ response would be by a guess andcheck methodology. This would require a manual speed adjustment and waitfor a settling of physiological parameters such as pressure and flow.This is done using averaged parameters and cannot be translated to aninstantaneous or real-time application.

SUMMARY

The techniques of this disclosure generally relate to a system andmethod for automating speed changes in a rotary blood pump to produce adesired pressure-flow relationship.

In one aspect, the present disclosure provides for a method ofcontrolling an implantable blood pump having a predefined hydraulicperformance. The method includes at least from the group consisting ofestimating and measuring an instantaneous flow rate during operation ofthe blood pump at a predetermined rotational speed of an impeller of theblood pump, the instantaneous flow rate including a plurality of flowrate data points. The plurality of flow rate data points define atrajectory around at least one from the group consisting of anoperational point of a predefined pressure-flow curve associated withthe predetermined rotational speed of the impeller of the blood pump anda target operational point of a target pressure-flow curve differentthan the predefined pressure-flow curve. The predetermined rotationalspeed of the impeller is adjusted until the plurality of flow rate datapoints define a predetermined trajectory around at least one of theoperational point and the target operational point.

In another aspect, the disclosure provides for estimating an averageflow rate during operation of the blood pump at the predeterminedrotational speed and adjusting the predetermined rotational speed of theimpeller of the implantable blood pump until the estimated average flowrate is substantially equal to a target average flow rate.

In another aspect, the disclosure provides for correlating thetrajectory of the plurality of flow rate data points to a pump preloadsensitivity.

In another aspect, the disclosure provides for correlating thetrajectory of the plurality of flow rate data points to a pump conditionresistant to high pressure conditions.

In another aspect, the disclosure provides for correlating thetrajectory of the plurality of flow rate data points to a pump conditionresistant to retrograde flow.

In another aspect, the disclosure provides that the instantaneous flowrate is estimated.

In another aspect, the disclosure provides that the instantaneous flowrate is measured.

In another aspect, the disclosure provides that the plurality of flowrate data points define the trajectory around the operational point ofthe predefined pressure-flow curve associated with the predeterminedrotational speed of the impeller of the blood pump.

In another aspect, the disclosure provides that the plurality of flowrate data points define the target operational point of the targetpressure-flow curve different than the predefined pressure-flow curve.

In one aspect, the disclosure provides for a system for controlling animplantable blood pump having a predefined hydraulic performance. Thesystem includes a controller in communication with the implantable bloodpump, the implantable blood pump having an impeller, the controllerbeing configured to at least from the group consisting of estimate andmeasure an instantaneous flow rate during operation of the blood pump ata predetermined rotational speed of an impeller of the blood pump, theinstantaneous flow rate including a plurality of flow rate data points.The plurality of flow rate data points define a trajectory around atleast one from the group consisting of an operational point of apredefined pressure-flow curve associated with the predeterminedrotational speed of the impeller of the blood pump and a targetoperational point of a target pressure-flow curve different than thepredefined pressure-flow curve. The controller is further configured toadjust the predetermined rotational speed of the impeller until theplurality of flow rate data points define a predetermined trajectoryaround at least one of the operational point and the target operationalpoint.

In another aspect, the disclosure provides that the implantable bloodpump includes a flow meter downstream from the impeller, and wherein thecontroller is configured to measure the instantaneous flow rate.

In another aspect, the disclosure provides that the instantaneous flowrate is estimated.

In another aspect, the disclosure provides that the controller isfurther configured to estimate an average flow rate during operation ofthe blood pump at the predetermined rotational speed and adjust thepredetermined rotational speed of an impeller of the implantable bloodpump until the estimated average flow rate is substantially equal to atarget average flow rate.

In another aspect, the disclosure provides that the controller isfurther configured to correlate the trajectory of the plurality of flowrate data points to a pump preload sensitivity.

In another aspect, the disclosure provides that the controller isfurther configured to correlate the trajectory of the plurality of flowrate data points to a pump condition resistant to high pressureconditions.

In another aspect, the disclosure provides that the controller isfurther configured to correlate the trajectory of the plurality of flowrate data points to a pump condition resistant to retrograde flow.

In another aspect, the disclosure provides that the instantaneous flowrate is measured.

In another aspect, the disclosure provides that the plurality of flowrate data points define the trajectory around the operational point ofthe predefined pressure-flow curve associated with the predeterminedrotational speed of the impeller of the blood pump.

In another aspect, the disclosure provides that the plurality of flowrate data points define the target operational point of the targetpressure-flow curve different than the predefined pressure-flow curve.

In one aspect, the disclosure provides for a system for controlling animplantable blood pump having a predefined hydraulic performance. Thesystem includes a controller in communication with the implantable bloodpump, the implantable blood pump having an impeller, the controllerbeing configured to at least from the group consisting of estimate andmeasure an instantaneous flow rate during operation of the blood pump ata predetermined rotational speed of an impeller of the blood pump, theinstantaneous flow rate including a plurality of flow rate data points.The plurality of flow rate data points define a trajectory around atleast one from the group consisting of an operational point of apredefined pressure-flow curve associated with the predeterminedrotational speed of the impeller of the blood pump and a targetoperational point of a target pressure-flow curve different than thepredefined pressure-flow curve. The controller further correlates thetrajectory of the plurality of flow rate data points to a pump conditionresistant to high pressure conditions and adjusts the predeterminedrotational speed of the impeller until the plurality of flow rate datapoints define a predetermined trajectory around at least one of theoperational point and the target operational point. The controllerfurther estimates an average flow rate during operation of the bloodpump at the predetermined rotational speed and adjusts the predeterminedrotational speed of an impeller until the estimated average flow rate issubstantially equal to a target average flow rate.

The details of one or more aspects of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the techniques described in this disclosurewill be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is an exploded view showing an exemplary HVAD blood constructedin accordance with the principles of the present application;

FIG. 2 is a graph showing predetermined pressure-flow (“HQ”) curvesassociated with the HVAD pump and a target HQ curve superimposed on thepredetermined HQ curves;

FIG. 3 is graph showing an operational point along a target HQ curve(solid line) and the trajectory (dashed line) of a plurality of flowrate data points around an operational point of a blood pump for apredetermined constant speed; and

FIG. 4 is a graph showing a plurality of operational points along atarget HQ curve and the trajectory (ellipses) of a plurality of flowrate data points around the associated operational point.

DETAILED DESCRIPTION

Before describing in detail exemplary embodiments, it is noted that theembodiments reside primarily in combinations of apparatus components andprocessing steps related to method for automating speed changes in arotary blood pump to produce a desired pressure-flow relationship.Accordingly, the system and method components have been representedwhere appropriate by conventional symbols in the drawings, showing onlythose specific details that are pertinent to understanding theembodiments of the present disclosure so as not to obscure thedisclosure with details that will be readily apparent to those ofordinary skill in the art having the benefit of the description herein.

As used herein, relational terms, such as “first” and “second,” “top”and “bottom,” and the like, may be used solely to distinguish one entityor element from another entity or element without necessarily requiringor implying any physical or logical relationship or order between suchentities or elements. The terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the concepts described herein. As used herein, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes” and/or“including” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

In embodiments described herein, the joining term, “in communicationwith” and the like, may be used to indicate electrical or datacommunication, which may be accomplished by physical contact, induction,electromagnetic radiation, radio signaling, infrared signaling oroptical signaling, for example. One having ordinary skill in the artwill appreciate that multiple components may interoperate andmodifications and variations are possible of achieving the electricaland data communication.

In one or more examples, the described techniques may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored as one or more instructions orcode on a computer-readable medium and executed by a hardware-basedprocessing unit. Computer-readable media may include non-transitorycomputer-readable media, which corresponds to a tangible medium such asdata storage media (e.g., RAM, ROM, EEPROM, flash memory, or any othermedium that can be used to store desired program code in the form ofinstructions or data structures and that can be accessed by a computer).

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor” as used herein may refer toany of the foregoing structure or any other physical structure suitablefor implementation of the described techniques. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

Referring now to the drawings in which like reference designators referto like elements there is shown in FIG. 1 an exemplary blood pumpconstructed in accordance with the principles of the present applicationand designated generally “10.” The blood pump 10 according to oneembodiment of the disclosure includes a static structure or housing 12which houses the components of the blood pump 10. In one configuration,the housing 12 includes a lower housing or first portion 14, an upperhousing or second portion 16, and an inlet portion or inflow cannula 18which includes an outer tube 18 a and an inner tube 18 b. The firstportion 14 and the second portion 16 cooperatively define a voluteshaped chamber 20 having a major longitudinal axis 22 extending throughthe first portion and inflow cannula 18. The chamber 20 defines a radiusthat increases progressively around the axis 22 to an outlet location onthe periphery of the chamber 20. The first portion 14 and the secondportion 16 define an outlet 24 in communication with chamber 20. Thefirst portion 14 and the second portion 16 also define isolated chambers(not shown) separated from the volute chamber 20 by magneticallypermeable walls.

The inflow cannula 18 a-18 b (“18”) is generally cylindrical and extendsfrom first portion 14 and extends generally along axis 22. The inflowcannula 18 has an upstream end or proximal end 26 remote from secondportion 16 and a downstream end or distal end 28 proximate the chamber20. The parts of the housing 12 mentioned above are fixedly connected toone another so that the housing 12 as a whole defines a continuousenclosed flow path. The flow path extends from upstream end 26 at theupstream end of the flow path to the outlet 24 at the downstream end ofthe flow path. The upstream and downstream directions along the flowpath are indicated by the arrows U and D respectively. A post 30 ismounted to first portion 14 along axis 22. A generally disc shapedferromagnetic rotor 32, for example, and impeller with a central hole34, is mounted within chamber 20 for rotation about the axis 22. Rotor32 includes a permanent magnet and also includes flow channels fortransferring blood from adjacent the center of the rotor 32 to theperiphery of the rotor 32. In the assembled condition, post 30 isreceived in the central hole of the rotor 32. A first stator 36 having aplurality of coils may be disposed within the first portion 14downstream from the rotor 32. The first stator 36 may be axially alignedwith the rotor along axis 22 such that when a current is applied to theplurality of coils in the first stator 36, the electromagnetic forcesgenerated by the first stator 36 rotate the rotor 32 and pump blood. Asecond stator 38 may be disposed within the second portion 16 upstreamfrom the rotor 32. The second stator 38 may be configured to operate inconjunction with or independently of the first stator 36 to rotate therotor 32.

An electrical connector 41 is provided on first portion 14 forconnecting the coils to a source of power such as a controller 39. Thecontroller 39 is arranged and configured to apply power to the coils ofthe pump to create a rotating magnetic field which spins rotor 32 aroundaxis 22 in a predetermined first direction of rotation, such as thedirection R indicated by the arrow in FIG. 1, i.e., counterclockwise asseen from the upstream end of inflow cannula 18. In other configurationsof the blood pump 10, the first direction may be clockwise. Rotation ofthe rotor 32 impel blood downstream along the flow path so that theblood, moves in a downstream direction D along the flow path, and exitsthrough the outlet 24. During rotation, hydrodynamic and magneticbearings (not shown) support the rotor 32 and maintain the rotor 32 outof contact with the surfaces of the elements of the first portion 14 andthe second portion 16 during operation. A first non-ferromagnetic disk40 may be disposed within the first portion 14 downstream from the rotor32 between the first stator 36 and the rotor 32 and a secondnon-ferromagnetic disk 42 may be disposed upstream from the rotor 32within the second portion 16 between the second stator 38 and the rotor32. The general arrangement of the components described above may besimilar to the blood pump 10 used in the MCSD sold under the designationHVAD by HeartWare, Inc., assignee of the present application. Thearrangement of components such as the magnets, electromagnetic coils,and hydrodynamic bearings used in such a pump and variants of the samegeneral design are described in U.S. Pat. Nos. 6,688,861; 7,575,423;7,976,271; and 8,419,609, the disclosures of which are herebyincorporated by reference herein. It is contemplated pumps having asingle stator as described, for example, in U.S. Pat. No. 8,007,254 andU.S Patent Application Publication No. 2015/0051438 A1, sold under thedesignation MVAD by HeartWare, Inc., assignee of the presentapplication, are contemplated to be used with method of the presentapplication.

Referring now to FIG. 2, a plurality of predefined pressure-flow or HQcurves 44 are shown for the blood pump 10. The HQ curves 44 define apredefined pump hydraulic performance regardless of the rotational speedof the rotor or impeller 32 of the pump 10 when operating in closedloop. In other words, each curve of the HQ curves 44 represents theexpected pressure-flow profile for a given constant speed of theimpeller 32 and constant viscosity of the fluid flowing through the pump10, for example, blood. The HQ curves 44 indicate that as flow increasesfrom 0-10 LPM the pressure-head, i.e. the differential pressure betweenthe pressure upstream of the inflow cannula 18 and downstream of thepump 10 at outlet 24, decreases. Operational points 46, indicated bybullets in FIG. 2, are average reference points to estimate or otherwisedetermine the average pressure-head and average flow at a given constantspeed of the impeller 32 that is associated with the HQ curve 44. Forexample, as shown in FIG. 2, operational point 46 a is expected toproduce an average flow of about 8 LPM at an average pressure-head ofabout 50 mmHg. Thus, based on the predefined HQ curves, if the speed ofthe impeller 32 and the flow is known, the pressure-head may becalculated.

Continuing to refer to FIG. 2, a target HQ curve 48 represents a targetHQ hydraulic performance different than the HQ curve 44 with targetoperational points 48 a. For example, target operational point 48 a isexpected to produce an average flow of about 7 LM at an average pressureof about 80 mmHg, which is different than the predefined HQ curve at thegiven constant speed and viscosity. To achieve the target HQ curve 48,the controller 39 may modulate or otherwise adjust the speed of theimpeller 32 to average speeds that results in the target HQ curve 48 andtarget operational point 48 a.

Referring now to FIG. 3, target HQ curve 48 is shown with a targetoperational point 48 a. The elliptical orbit around target operationalpoint 48 a represents the instantaneous flow rate measurements orestimations made by the controller 39 to derive at the averageoperational point 48 a. The instantaneous flow rate may be estimated bymethods known in the art and may include, but are not limited to, themethod of estimating flow in a blood pump disclosed in U.S. Pat. Nos.8,897,873, 9,511,179, and 8,961,390, the entirety of which areincorporated herein by reference. Alternatively, instantaneous flow maybe measured by including a flow meter downstream from outlet 24. Theellipse and arrows around the target operational point 48 a indicate theboundary of the instantaneous flow rate estimations and/or measurementsand the direction of the plurality of instantaneous flow points aroundthe target operational point 48 a. For example, it is expected that theinstantaneous flow points fall within the ellipse and the average ofthose points establishes the target operational point 48 a. The arrowsindicate the direction of those instantaneous points to identify trendsand those trends can be manipulated for each target operational point 48a.

Referring now to FIGS. 3-4, the slope of the ellipse is indicative of atrajectory of the instantaneous points that comprise the average targetoperating point 48 a. For example, as shown in FIG. 3, targetoperational point 48 b defines an ellipse of instantaneous points thatdefine and average represented by target operational point 48 b. Thetrajectory of the ellipse defines a slope indicated by the dashed lines.The trajectory of the ellipse may be indicative of a pump characteristicand/or adverse events. For example, as shown in FIG. 4, the trajectoryof the ellipse around lower flow regions, as shown with respect totarget operational point 48 c, may be an operational point that preventshigh pressure conditions and prevent retrograde flow in the pump 10. Aflatter ellipse trajectory, as shown associated with target operationalpoint 48 d may increase preload sensitivity. Thus, the target HQ curve48 may have a number of target operational points 48 a that may betailored for desired conditions. In another words, the controller 39 mayautomatically adjust the rotational speed of the impeller 32 to createthe desired trajectory of instantaneous flow points and also adjust theimpeller 32 to operate at the average operational point along a targetHQ curve 48. For example, the controller 39 slew rates may be modifiedto support the desired speed changes in the impeller 32. Similarly, thedesired trajectory around an operational point 46 along HQ curve 44 mayalso be created by adjusting the predetermined speed of the impeller 32.

In an exemplary method of operation, the instantaneous flow is estimatedor measured during operation of the blood pump at a predeterminedrotational speed of an impeller 32 of the blood pump 10. For example,the flow may be measured while the impeller 32 is rotating at a speed of2800 RPM, or alternatively when the pump is operating an impeller speedthat creates a target HQ curve 48. The instantaneous flow rate includesa plurality of flow rate data points that define an ellipse around theaverage of those data points. The average of the instantaneous flowpoints define either a predefined operational point 46 associated withthe predefined pressure-flow curve 44, or the rotational speed of theimpeller 32 may have been adjusted to create a target operational point48 that is not associated with the predefined pressure-flow curve. Thepredetermined rotational speed of the impeller 32 is adjusted until theplurality of flow rate data points define a predetermined trajectoryaround a target operating point 48 or the operational point 46. Thus,the method provides for operational point control whether the pump 10 isoperating at an operational point 46 associated with the predefinedpressure-flow curves, or when the pump 10 is operating at a targetoperational point 48 a under a target pressure-flow curve 48. It isfurther contemplated that the above method is applicable not only whenthe pump 10 is operating under static conditions, but also underpulsatile conditions.

It should be understood that various aspects disclosed herein may becombined in different combinations than the combinations specificallypresented in the description and accompanying drawings. It should alsobe understood that, depending on the example, certain acts or events ofany of the processes or methods described herein may be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,all described acts or events may not be necessary to carry out thetechniques). In addition, while certain aspects of this disclosure aredescribed as being performed by a single module or unit for purposes ofclarity, it should be understood that the techniques of this disclosuremay be performed by a combination of units or modules associated with,for example, a medical device.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A method of controlling an implantable blood pumphaving a predefined hydraulic performance, comprising: estimating ormeasuring an instantaneous flow rate during operation of the blood pumpat a predetermined rotational speed of an impeller of the blood pump,the instantaneous flow rate including a plurality of flow rate datapoints; the plurality of flow rate data points defining a trajectoryaround at least one from the group consisting of an operational point ofa predefined pressure-flow curve associated with the predeterminedrotational speed of the impeller of the blood pump and a targetoperational point of a target pressure-flow curve different than thepredefined pressure-flow curve; and adjusting the predeterminedrotational speed of the impeller until the plurality of flow rate datapoints define a predetermined trajectory around at least one of theoperational point and the target operational point.
 2. The method ofclaim 1, further comprising: estimating an average flow rate duringoperation of the blood pump at the predetermined rotational speed; andadjusting the predetermined rotational speed of the impeller of theimplantable blood pump until the estimated average flow rate issubstantially equal to a target average flow rate.
 3. The method ofclaim 1, further comprising correlating the trajectory of the pluralityof flow rate data points to a pump preload sensitivity.
 4. The method ofclaim 1, further comprising correlating the trajectory of the pluralityof flow rate data points to a pump condition resistant to high pressureconditions.
 5. The method of claim 1, further comprising correlating thetrajectory of the plurality of flow rate data points to a pump conditionresistant to retrograde flow.
 6. The method of claim 1, wherein theinstantaneous flow rate is estimated.
 7. The method of claim 1, whereinthe instantaneous flow rate is measured.
 8. The method of claim 1,wherein the plurality of flow rate data points define the trajectoryaround the operational point of the predefined pressure-flow curveassociated with the predetermined rotational speed of the impeller ofthe blood pump.
 9. The method of claim 1, wherein the plurality of flowrate data points define the target operational point of the targetpressure-flow curve different than the predefined pressure-flow curve.